1. Field of the Invention
The present invention relates to a fuel nozzle, a gas turbine combustor with the same, and a gas turbine with the same. More particularly, the present invention relates to cooling a dual fuel nozzle used by switching between oil and gas.
2. Description of Related Art
A gas turbine combustor in a gas turbine may be provided to burn gas fuel or oil fuel by switching between the gas fuel and the oil fuel, in which the oil fuel, the gas fuel, and combustion air are delivered. Hot combustion gas generated by burning the fuel in the gas turbine combustor is delivered into the gas turbine to drive the gas turbine. At the start of combustion, the oil fuel or the gas fuel may be delivered into a fuel nozzle disposed at the axial center of the gas turbine combustor for ignition.
Here, the fuel nozzle is arranged in the gas turbine combustor so that the axial direction of an approximately cylindrical fuel nozzle body is the same as the direction of air flow in the gas turbine combustor. In the approximately cylindrical fuel nozzle body, gas fuel passages are provided at almost equal intervals in its circumferential direction. Also, a circular air passage is provided between an external cylinder covering the outer circumference of the fuel nozzle body and the outer circumferential wall of the fuel nozzle body.
The fuel nozzle formed as described above injects the incoming air from the air passage approximately obliquely inward toward the axial center of the fuel nozzle body from an air injection port provided in the vicinity of a distal end portion of the fuel nozzle so as to deliver the air into the gas turbine combustor.
The gas fuel delivered to the distal end portion of the fuel nozzle through the gas fuel passage is injected approximately obliquely outward toward the axial center of the fuel nozzle body from a gas injection port provided in the vicinity of the distal end portion.
The oil fuel is delivered through an oil fuel nozzle accommodated in a cylindrical space formed by the inner wall of the approximately cylindrical fuel nozzle body and is injected into the gas turbine combustor from an injection port provided at the center of a distal end portion of the oil fuel nozzle.
Thus, the air and the gas fuel or the oil fuel are burnt by being injected into the gas turbine combustor from the distal end portion of the fuel nozzle and are ignited.
At the distal end portion of the fuel nozzle, hot air delivered from the air passage is injected while the gas fuel with a lower temperature than the air delivered from the gas fuel passage formed to closer to the axial center of the fuel nozzle than the air passage is injected. Therefore, the difference in temperature between the outer circumferential side (the side close to the air passage) and the inner circumferential side (the side close to the gas fuel passage) of the fuel nozzle body sandwiched between the gas fuel passage and the air passage becomes large, which causes the difference in thermal elongation. Thus, a crack may be generated on a welded portion of the distal end portion of the fuel nozzle.
When only the gas fuel is used, the oil fuel nozzle is removed. Accordingly, a cylindrical space along the central line in the axial direction of the fuel nozzle, which is generated by removing the oil fuel nozzle, is exposed to the hot combustion gas. A cap for sealing the space from the distal end portion of the fuel nozzle is provided to prevent a crack generated on the welded portion of the distal end portion of the fuel nozzle due to the hot fuel gas introduced into the space. The cap is exposed to the hot combustion gas, and thus needs to be cooled (for example, Japanese Unexamined Patent Application, Publication No. Hei 10-205757).
In order to cool the cap provided on the distal end portion of the fuel nozzle, air may be introduced into the cap from an external air system.
Japanese Unexamined Patent Application, Publication No. 2002-71135 discloses cooling the cap by deflecting air compressed by a compressor provided in a gas turbine to deliver the air into the space of the fuel nozzle and by effusing the air from the distal end portion of the fuel nozzle through an effusion hole provided on a distal end surface of the cap from the space.
However, when air is introduced into the cap from the external air system to cool the cap, pipes or the like for introducing the outer air are complicated.
In the invention disclosed in Japanese Unexamined Patent Application, Publication No. 2002-71135, the oil fuel nozzle is removed when only the gas fuel is used and then the cap formed with an air passage for cooling is required to be provided on the distal end portion of the fuel nozzle. Thus, considerable cost is required.
The present invention has been made in view of the above-described circumstances. It is an object to provide a fuel nozzle capable of easily cooling a distal end portion of the fuel nozzle at low cost, and a gas turbine combustor with the fuel nozzle, and a gas turbine with the gas turbine combustor.